1. Technical Field
This invention relates to MEMS devices, and more particularly to a microfabricated nanopositioner capable of movement in six degrees of freedom.
2. Background Information
Throughout this application, various publications, patents and published patent applications are referred to by an identifying citation. The disclosures of the publications, patents and published patent applications referenced in this application are hereby incorporated by reference into the present disclosure.
A wide variety of micro-fabricated nanopositioners are known in the art. These devices are operated by a variety of actuation species, including electrostatic, electromagnetic, electrothermal, and piezoelectric.
These nanopositioners are motion systems capable of positioning a sample in space with nanometer precision (e.g., within tens of nanometers). Nanopositioners can operate in multiple axes, to provide accurate orientation in many degrees-of-freedom (DOF). Multi-axis meso-scale (e.g., 5 to tens of millimeter- or coin-sized) nanopositioners may enable high-speed and precise positioning and measurement in the biological sciences, data storage, probing equipment for nano-scale measurements, and nanomanufacturing processes. Emerging applications in these fields would benefit from portable, multi-axis, nanometer-level positioning over a range of tens-of-microns at speeds of hundreds to thousands of Hertz.
Relatively large, macro-scale nanopositioners can position large and small objects over a range of hundreds of microns with nanometer precision in up to six degrees-of-freedom, but their relatively large masses limit their natural frequencies to 10-100 Hz. Many of these devices operate under closed loop control, require high-voltage power supplies, and often cost thousands of dollars. In addition, thermal fluctuations can generate relatively large position errors in macro-scale machines. The positioning of small-scale samples, such as probe tips, cells, thin-film samples, and micro-optics, often does not require the force and stroke capabilities of these large nanopositioners.
The mismatch between the length/time scales (i.e., range of motion and speed of movement) of macro-scale positioners and many nano-scale phenomena limits the use of these nanopositioners in future small-scale applications. For instance, nano-scale electro-machining is a serial process requiring as little as several hundreds of microseconds to remove cubic-nanometers of material. Sample moves of several microns should be executed in milliseconds and with nanometer precision in order to make the nano-machining process practical and time efficient. As another example, probe-based data storage may also benefit from millisecond move times and nanometer precision in order to improve data rates and storage density.
However, such small scale nanopositioners have not been previously developed. Although much of the physics scale from macro- to micro-scale systems, microfabrication constraints fundamentally change the design methodology for small-scale nanopositioners. Assembly and fabrication methods used to realize macro-scale electromagnetic (EM) actuators are generally unsuitable for building micro- and meso-scale (i.e., microfabricated) actuators.
Contrary to the conventional approaches used to fabricate macro-scale actuators, microfabricated micro-coil structures are limited to generally planar geometries. For example, a planar EM actuator is disclosed in U.S. Pat. No. No. 6,369,400 (the '400 patent). This patent discloses a magnetic scanning or positioning system fabricated using conventional microlithographic techniques. The system includes a base equipped with magnets, a movable platform equipped with electrical coils, and suspension elements providing an elastic connection between the movable platform and the supporting base. The electrical coils are positioned flat on the movable platform, to form a substantially flat arrangement with the movable platform. The '400 patent teaches that combining the flat arrangement with the flat supporting base yields a scanning or positioning system which is potentially compact, lightweight and flat and which features fast response, low power consumption and a relatively wide range of motion, e.g., between 1 μm and 10 mm. The device is taught to be useful in the field of scanning probe microscopy or in the field of data storage or imaging.
A drawback, however, of this approach is that the coils are rigidly coupled to the movable stage, which results in a relatively large moving mass. This large mass and its associated low resonance frequency, results in a relatively low bandwidth, i.e., slow response time. This configuration also results in a relatively large footprint, which tends to undesirably limit component density. In addition, the system as shown is limited to motion in 5 DOF (not 6), and suffers from a relatively complex fabrication process.
Realizing six DOF, open-loop positioning, with precision to within tens of nanometers at speeds of hundreds to a thousand Hz or more will require a departure from the traditional micro-scale and macro-scale EM actuator design.
In light of the foregoing, a need exists for a meso-scale, multi-axis nanopositioning system capable of operating at hundreds of Hz to kilohertz frequencies with tens-of-microns of stroke, and nanometer level precision.